Process for direct oxidation of propylene to propylene oxide and large particle size titanium silicalite catalysts for use therein

ABSTRACT

Large crystals of titanium silicalite or intergrowths of intergrown smaller crystals, having a mean particle size greater than 2 μm, have been found catalytically effective at commercially reasonable rates for the epoxidation of olefins in the presence of hydrogen peroxide. Crystals synthesized with a silica source having a low sodium content exhibit high levels of production and selectivity. The crystals have a low attrition rate and are easily filterable from a product stream.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the synthesis of propylene oxide fromhydrogen peroxide in the presence of a titanium silicalite catalyst, orfrom hydrogen/oxygen mixtures in the presence of a commercially viablenoble metal-treated titanium silicalite catalyst.

2. Background Art

Propylene oxide is an important alkylene oxide of commerce. Largeamounts of propylene oxide are used, inter alia, for the preparation ofnonionic polyether surfactants and of polyether polyols for manufactureof polyesters and other polymers, but in particular for polyols formanufacture of polyurethanes, the latter including both homopolymericpolyoxypropylene polyols and copolymeric polyols prepared using otheralkylene oxides, particularly ethylene oxide, in addition to propyleneoxide. Propylene oxide also has numerous other uses in organicsynthesis.

Older methods of propylene oxide production employed the“epichlorohydrin” process, a process which employs toxic chlorine, andgenerates numerous chlorine-containing byproducts which presentenvironmental concerns but is still in use today. Several “coproduct”processes have been disclosed and/or implemented. In one majorcommercial process, indirect oxidation of propylene by ethylbenzeneoxidation products to form propylene oxide yields styrene as a majorcoproduct. In both this as well as other coproduct processes, theeconomic value of the coproduct has a great effect on the overallprocess economics. The value of the coproducts may at times byundesirably low. Thus, it is desirable to employ a process which doesnot rely on coproduct economics to produce propylene oxide.

A “direct” method of propylene oxide production has long been sought. Insuch “direct” methods, propylene oxide is produced by oxidation ofpropylene with oxygen or with a “simple” oxidizing precursor such ashydrogen peroxide, without the use of significant amounts ofco-reactants and concomitant generation of co-products from theseco-reactants. Even though a great deal of research has been expended inthese efforts, “direct” production of propylene oxide has not heretoforebecome a commercial reality.

In U.S. Pat. No. 5,401,486, it is disclosed that propylene oxide may beproduced by the “direct” oxidation of propylene by hydrogen peroxide inthe presence of a titanium silicalite catalyst, citing EP A-100,118.However, the latter indicates that the principle products of olefinoxidation are ethers, with olefin oxides prepared only in minor amounts.The titanium silicalite useful in such processes, despite the relativelylow yield of olefin oxides, has been generally acknowledged by the artto be limited to exceptionally small titanium silicalite crystalssubstantially free of the anatase form of titanium silicalite. Thesecrystals are about 0.2 μm or less in size. Since the catalysts areheterogenous catalysts, use of larger particle size catalysts, withtheir decreased surface area, should result in a considerable decreaseof activity and product yield in the oxidation of alkenes. For example,the rate of oxidation of linear alkanols employing titanium silicaliteshas been shown to be reduced as crystal size of the titanium silicaliteis increased. See, e.g., “Oxidation of Linear Alcohols with HydrogenPeroxide Over Titanium Silicalite 1,” A. Van der Pol et al., SchuitInstitute of Catalysis, Eindhoven University of Technology, APPL. CATAL.A., 106(1) 97-113 (1993), which indicates that a particle size less than0.2 microns is necessary to obtain maximum catalyst activity. See alsoU.S. Pat. No. 6,106,803, which indicates that high catalytic activitycan only be obtained with small primary crystals of titanium silicalite.The U.S. Pat. No. 6,106,803 patentees teach preparing small primarycrystals and using these crystals to form granulates of larger size byspray-drying. These and other publications have discouragedinvestigation of the use of large titanium silicalite crystals.

Other references which relate more directly to olefin epoxidationindicate that selectivity and hydrogen peroxide conversion efficiencyare decreased by the presence of anatase in the titanium silicalitecatalyst. See, e.g., “Preparation of TS-1 Zeolite Suitable forCatalyzing the Epoxidation of Propylene,” H. Gao et al., ShanghaiResearch Institute of Petrochemical Technology, Shanghai, PeoplesRepublic of China, Shiyou Xuebao, Shiyou Jiagong (2000) 16 (3), p.79-84; and “Synthesis and Physicochemical Properties of ZeolitesContaining Framework Titanium,” C. Dartt et al., California Institute ofTechnology, Pasadena, Calif., MICROPOROUS MATTER, 2 (5) p. 425-437(1994).

However, use of small titanium crystals, e.g. those having mean sizes ofabout 0.2 μm or less is highly problematic in commercial epoxidation ofalkenes. In fixed bed processes, the small particle size creates anenormous pressure drop which renders the process unworkable, while inslurry processes, separation of the catalyst from the liquid reactorcontents is extremely difficult. Moreover, due to the attrition ofparticulate catalysts in commercially useful reactors, the particle sizedecreases over time, eventually plugging filters designed to recover andrecirculate catalyst back to the reactor. As a result, although thecatalyst activity of small particle size catalysts is reasonably high, acommercial process employing such catalysts is not practical.

To improve the longevity of the olefin epoxidation process, smalltitanium silicalite crystals have been conglomerated into formedparticles of larger size through the use of binders, as taught, forexample, by U.S. Pat. Nos. 5,500,199 and 6,106,803. However, suchconglomerated catalysts suffer from several defects. The binder, thoughporous, will necessarily obscure portions of the zeolite structure, thuseffectively removing such portions as catalytic sites in the reaction.Unless the binder has high adhesive and cohesive strength, the formedparticles will again be subject to attrition as the conglomerates breakapart. Increasing binder content can minimize attrition, although thelikelihood of obscuring catalytic sites is then higher. Moreover, thecatalyst is essentially “diluted” by the binder on a weight/weightbasis, thus requiring greater amounts of catalyst for the same epoxideproduction rate.

It would be desirable to directly epoxidize propylene in the presence oflarge titanium silicalite crystals which exhibit high activity, lowattrition rates, and freedom from use of binders, and which do not causerapid plugging of catalyst filter elements.

SUMMARY OF THE INVENTION

It has now been surprisingly discovered that large sized crystals oftitanium silicalite and crystal intergrowths thereof may be used inalkene epoxidation at commercially useful epoxidation rates despite theprejudice of the art against the use of such large sized particles. Ithas been further surprisingly discovered that the silica source materialcan markedly affect catalytic activity. Alkene epoxidation processesemploying large crystals and intergrowths generate fines much lessrapidly, and thus alkene epoxidations employing such catalysts can runfor extended periods without shutdown, and with considerably lessaddition of new catalyst to the process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning election micrograph of titanium silicaliteintergrowths prepared according to one aspect of the invention.

FIG. 2 is a scanning electron micrograph of non-intergrown large singlecrystal titanium silicalite prepared according to a further embodimentof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention pertains to alkene epoxidation in the presence oftitanium silicalite catalyst particles having an average particle sizeof greater than 2 microns. The size of the particles can be measured byscaling from scanning electron micrographs or via methods which arebased on laser dispersion methods. Epoxidation in the subject inventionprocess may be by hydrogen peroxide or by a mixture of hydrogen andoxygen when a suitable noble metal-treated catalyst is used. As usedherein, the term “epoxidation” refers to processes using either set ofepoxidizing reactants set forth above unless indicated otherwise. Theuse of hydrogen and oxygen may be termed an “in situ” process, sincehydrogen peroxide is generated in situ. In the latter process, thepreferred catalyst is a palladium-treated titanium silicalite, althoughother palladium catalysts and other metal catalysts may be used inconjunction with titanium silicalite epoxidation catalysts. Examples ofsuch metal catalysts include but are not limited to Ni, Pd, Pt, Cu, Ag,and Au. Noble metal catalysts are presently preferred.

The alkene which is epoxidized is a C₃ or higher alkene, preferablypropylene, although the process is also useful with other alkenes suchas C₄₋₂₀ alkenes, more preferably C₄₋₈ alkenes, and yet more preferablyC₄ alkenes such as 1-butene and 2-butene. Cyclic alkenes such ascyclohexene and cyclopentene are also useful, as are dienes andpolyenes, for example 1,3-butadiene. The epoxidation preferably takesplace continuously, for example in continuous stirred tank reactors(CSTR), tubular reactors, fixed bed and fluidized reactors, and thelike. In such processes, alkene and epoxidizing agent are fed to thereactor and contacted with the solid titanium silicalite catalyst. Thetemperature is adjusted to achieve a reasonable reaction rate withoutgeneration of byproduct types and amounts which would render sustainedoperation problematic. Reaction temperatures of 25° C. to 100° C. arepreferred, more preferably 30° C. to 80° C., and most preferably 40° C.to 70° C. Selection of the reaction temperature, reactor pressure,byproduct separation, and product purification are easily made by oneskilled in the art.

Most preferably, the process is an in situ process employing hydrogen,oxygen, and a catalyst suitable for forming hydrogen peroxide in situ.Since hydrogen and oxygen are “permanent gases,” unreacted portions mayeasily be separated from the reactor and recycled. Palladium is thepreferred noble metal catalyst, but other noble metals which catalyzegeneration of hydrogen peroxide may be used as well, for example Pt, Au,and Ag. The noble metal may be supported on silica, thermoplastic beads,or any other convenient support. However, such supports occupy reactorvolume but do not catalyze olefin epoxidation. It has been found thatthe noble metal may be deposited onto titanium silicalite, and thecatalyst then performs the double function of both hydrogen peroxidegeneration and olefin epoxidation. Surprisingly, olefin epoxidationefficiency is maintained. Mixtures of untreated titanium silicalite andmetal-treated titanium silicalite may also be advantageously used.

The titanium silicalite catalysts useful in the present invention aretitanium silicalite single crystals and intergrowths having a meanparticle size greater than 2 μm. The term “intergrowth” should becontrasted with the prior use of “conglomerate” wherein sufficientbinder is added to form a shaped product, and wherein binder surroundssignificant portions of titanium silicalite crystals. The “intergrowths”of the present invention contain no binder to adhere crystals together.Most preferably, the crystals of the intergrowths are bound together bygrowth processes which yield an intertwined matrix of crystals withsubstantial integrity. An example of such intergrown crystals is shownin FIG. 1.

Single titanium silicalite crystals are generally flat rhombohedrons inshape. The minimum mean diameter (geometric) of single crystals acrosstheir major surfaces is 2 μm, but is preferably higher, i.e. 3-15 μm,more preferably 4-12 μm. At these large sizes, it is highly surprisingthat useful epoxidation rates can be maintained. Large single crystalsare generally flat rhombohedrons having an aspect ratio(length/thickness) of about 1 to 10, more preferably 1 to 6, and mostpreferably about 1 to 5. Small aspect ratios, i.e. 1-2, are mostpreferred. The thickness of the crystals is relatively small, i.e., inthe range of 0.3 to 5 μm, more preferably 0.4 to 3 μm, and mostpreferably 0.5 to 2 μm. An example of such crystals is shown in FIG. 2.

Use of intergrown titanium silicalite crystals for olefin epoxidationhas not been disclosed. Intergrown crystals are comprised substantiallyof titanium silicalite, with “primary” rhombohedral crystals ofrelatively small size, i.e., preferably less than 5.0 μm in size acrosstheir major faces, and preferably less than 4 microns. The intergrowthsare grown by processes wherein a considerable amount of intergrowth,“twinning,” etc., takes place, such that the intergrowths have meanparticle size (geometric mean in 3 dimensions) in excess of 2 μm, morepreferably in the range of 2-30 μm, and most preferably in the range of4-20 μm. Reference may be had to FIG. 1, where the mean particle size isabout 4-5 μm. Surprisingly, it has been found that such intergrowthshave even higher epoxidation performance than single crystals of thesame mean size.

Large titanium silicalite single crystals may be made by processes knownin the art, for example those disclosed by U.S. Pat. No. 5,401,486; EP119 130; EP 543,247; and STUDIES IN SURFACE SCIENCE, V. 84, p. 203-210.Small crystal titanium silicalite (i.e. 0.2 μm) synthesis is describedin U.S. Pat. No. 4,410,501. Most preferably a synthetic method asdisclosed herein is used. In the preparation of large single crystaltitanium silicalites, a range of particle sizes are generally produced.

For preparation of intergrown catalyst particles, any method whichresults in useful intergrowths having a particle (intergrowth) sizegreater than 2 μm may be used. It should be noted that such methods ofintergrowth preparation must not involve preparation of small crystalsfollowed by calcination with a binder as is used to form “shaped” or“formed” conglomerated catalyst particles. Rather, the crystal growthitself forms the intergrowth. Several examples of markedly differentintergrown “crystallites” are presented herein. These methods areexemplary and not limiting.

In one method of titanium silicalite single crystal growth, ahydrolyzable precursor of titanium and a silica source, or hydrolyzableprecursor(s) containing both silicon and titanium, are hydrolyzed inwater, preferably in the presence of ammonia, hydrogen peroxide and atetraalkylammonium compound such as a tetraalkylammonium halide. Thefirst part of the preparation is conducted at 1 atm and mildtemperatures, between 5° C. and 85° C., where “gel” is made. The secondpart of the preparation, a hydrothermal crystallization, is generallyconducted in a sealed autoclave at elevated temperature, i.e. 150° C. to200° C., under autogenous pressure. At the end of the growth period, forexample 100 to 200 hours, the pressure is then released.

For the preparation of titanium silicalite intergrowths, crystal growthpreferably occurs in a growth medium containing hydrolyzable titanium,hydrolyzable silica, and tetrapropylammonium hydroxide. Thecrystallization is preferably conducted at 130° C. to 200° C., morepreferably at about 150° C. to 180° C. for an extended period,preferably for 1 to 8 days. The crystals are somewhat round (polyhedric)in appearance, and clearly exhibit numerous crystals and crystal faces.Scanning electron micrographs of a typical intergrowth is shown in FIG.1. Preferred titanium and silica sources include alkyl- andalkoxy-functional siloxane/titanate copolymers. Such copolymers arecommercially available. By the term “hydrolyzable titanium/silicon”copolymer is meant a composition containing both silicon and titanium,with hydrolyzable functionality such that a titanium silicalite may beobtained by hydrolysis. Titanium and silicon-linked hydrolyzable groupsinclude, but are not limited to, alkoxy, hydrido, hydroxyl, halo, andlike groups. With respect to titanium, alkyl and aryl groups may bepresent as well.

It has further been discovered that the use of raw material sourceswhich are low in alkali metals and alkaline earth metals provide largecrystal titanium silicalite products with unexpectedly enhancedactivity. In particular, use of silica sources having less than 100 ppmsodium is highly desirable. Silica with even less sodium, for exampleabout 50 ppm or less, and with low aluminum and iron content is alsorecommended. Sources of such highly pure silica include fumed silicawhich is commercially available.

The titanium silicalite catalysts of the present invention arepreferably used in the previously described in situ process whereinhydrogen and oxygen rather than hydrogen peroxide are fed to the reactoras the source of oxygen for epoxidation. Under these conditions, thetitanium silicalite is altered to contain a noble metal, preferablypalladium, which may be applied to the titanium silicalite byconventional deposition processes. Any soluble palladium compound may beused in such deposition processes, or other methods of applying Pd maybe used. Tetraamine palladium dichloride and tetraamine palladiumdinitrate have both been used to successfully prepare palladium-treatedtitanium silicalite catalysts. Preferably, tetraamine palladiumdinitrate without an excess of ammonia is employed. The titaniumsilicalite may be treated, for example, with a solution of solublepalladium at 80° C. for 24 hours for the nitrate and 20° C. for 1 hourfor the chloride, followed by filtration and resuspension in deionizedwater. The product is then filtered and resuspended in deionized watertwice more. The palladium-treated product may be isolated, dried invacuum at 50° C. overnight, and calcined by heating in flowing 4 volumepercent oxygen in nitrogen to 110° C. (10° C./min), holding for 1 hour,and heating at 2° C./min to 150° C. followed by a 4 hour hold. Theweight percentage of palladium may range from 0.01 weight percent toabout 2 weight percent or higher, but is preferably 0.1 to about 0.8weight percent, more preferably 0.2 to 0.5 weight percent. Higherloadings of palladium can be accomplished by exposing apalladium-containing catalyst to further ion exchange from palladiumsolution followed by calcining, as described above. Further methods ofdepositing palladium and other catalytic metals may be found in the artof vehicular exhaust catalytic converters and other references dealingwith noble metal deposition. The methods described above are notlimiting.

Prior art catalysts have no commercial usefulness, as it is virtuallyimpossible to maintain continuous reactor operation with mean particlesizes of 0.2 μm or less productivity due to clogging of filters. Thepresent catalysts display an activity which is surprisingly high whenviewed in conjunction with the increased particle size. Even though thepresent process has not been optimized, epoxidation rates similar and insome cases superior to those of the prior art small size titaniumsilicalite crystals have been achieved. Processes employing the largercatalysts of the subject invention can run for extended periods withoutshutdown. Thus, even for catalysts with lower production rates, thefreedom from reactor down time makes these catalysts commerciallyviable.

Resistance to attrition is a necessary parameter for a commercialtitanium silicalite epoxidation catalyst. Attrition may be measured byperiodic sampling of solid catalyst from a reaction campaign, or may beassessed by an attrition test conducted in water or other suitablesolvent, and described below. The latter test has been shown toaccurately reflect attrition rate during epoxidation.

In the attrition test, a model reactor has a 3⅛ inch diameter I.D. andhas a 2 inch diameter Rushton turbine with 6 vanes, rotating at 650 RPM.The baffle cage has 4 strips, each) 5/16 inch wide. 50 μm of largecrystal TS-1 are charged with 500 ml of deionized water and agitated at20° C. No chemistry is conducted during the test. The titaniumsilicalite, when present as single crystals, is originally in the formof plates, normally with flat or slightly convex ends and straightsides. For example, in an actual test, measurements made directly fromelectron microscope images showed mean dimensions of 10.2×7.63×1.87microns, approximately in accordance with the values from an automatedlaser-based technique. Samples are subjected to electron microscopy andparticle size distribution measurement by laser dispersion, although anymethod of determining particle size and dimensions may be used. Thevolume-based median diameter (d_(vol, 50%)) and the number-based mediandiameter (d_(n,50%)) may be extracted from the size distribution data,and show a slow disintegration over time. The electron micrographs showa steady increase in the proportion of fines, mainly chips from thecorners and the edges of the titanium silicalite platelets.

The volume and number-based median particle sizes may be plotted as thelogarithms of their values against time in days, assuming that the sizeattrition is a first order process. A linear least squares fit yieldsthe following equations tracking size attrition for the exampledescribed above:

d_(vol,50%) (microns) = 10^(−0 0009t+0 9799) t = time in days Equivalentto −0.21%/day d_(n,50%) (microns) = 10^(−0 0005t+0 8974) t = time indays Equivalent to −0.12%/day

These relationships generate plots which are properly of negative slopeand of correct relative magnitude in the range of the data but intersectat high values of time. The particle size data at 0 hours were excludedfrom these curve fits because the first 24 hours of the test causedisintegration of loosely associated crystallites, which interferes withthe data. Using these equations, the particle sizes at 180 and 365 daysare projected to be as follows: d_(vol,50%) of 6.58 and 4.48 microns andd_(n,50%) of 6.42 and 5.19 microns. It should be noted thatconglomerates prepared by spray-drying 0.2 μm titanium silicalitecrystals with kaolin or alumina binders exhibited a substantially higherattrition rate, expressed as the rate of decline in the median particlediameter based on volume, averaging 18.6%/day, far too high to beuseful. The catalyst particles should have an attrition rate no higherthan 2% (loss) per day, preferably less than 1% per day, and morepreferably 0.5% or less per day.

The chemical efficiency of the various catalysts herein is assessedinitially by a screening test in batch mode. The “screening test” isperformed in a high pressure stainless steel autoclave, using hydrogenperoxide as the epoxidizing agent. The autoclave is charged with 40 g of84 wt. % methanol, 4.8% hydrogen peroxide, balance water, and 0.15 gtitanium silicalite-containing catalyst, the catalyst preferably beingsubstantially all titanium silicalite. The reactor is sealed and heatedto 50° C. and 19 g propylene injected. Agitation is provided by means ofa stir bar, revolving at 600 RPM (10 s⁻¹). After 0.5 h, the reactor isshock chilled to stop the reaction, and residual propylene degassed intoa gas bag. The propylene is weighed and analyzed, as is the aqueousphase remaining in the reactor. The hydrogen peroxide conversionefficiency, propylene oxide produced (“PO”) and propylene oxideequivalents produced (“POE”) are reported. By propylene oxideequivalents is meant propylene oxide and derivatives, i.e., propyleneglycol, acetol, 1-methoxy-2-propanol, 2-methoxy-1-propanol, dipropyleneglycol, tripropylene glycol, methoxydipropylene glycol, andmethoxytripropylene glycol, among others. The selectivities are reportedin percent as (mol PO/mol POE)×100%, measuring the relative extent of POring opening, and (mol POE/mol propylene consumed)×100%, measuring theselectivity of propylene conversion to POE. Another importantmeasurement of selectivity is (mol POE/mol hydrogen peroxideconsumed)×100% which measures the selectivity of hydrogen peroxideepoxidation of propylene to POE. In these experiments, the controlcatalyst for purposes of comparison is a titanium silicalite having aparticle size of 0.2 μm and a Ti content of 1.1 wt. %.

In a preferred commercial olefin epoxidation process, the titaniumsilicalite epoxidation catalyst is slurried in a reaction mixture liquidphase which may preferably comprise water, lower alcohols, alkylalcoholethers, ketones, and the like. The catalyst is preferably present in aslarge an amount which can be effectively maintained as a slurry, i.e.,without undue sedimentation to a static bed. The reactor is preferably adraft tube reactor, as disclosed in U.S. Pat. No. 5,972,661, howeverother reactor configurations are possible, including tubular reactorsand slurry reactors. Alternatively, the reactor may constitute a fixedbed of catalyst particles.

The reactant feed streams comprise, in addition to olefin, hydrogenperoxide and make-up solvent in the case of non-in-situ reactors, andhydrogen, oxygen, and make-up solvent in the case of in-situ reactors.Other reaction moderators, accelerators, buffers, etc. may be added asnecessary. For example, an alkali metal hydrogen carbonate feed streammay be added. Triammonium phosphate, diammonium phosphate, monoammoniumphosphate and mixtures thereof may be added as a feed stream. Whenhydrogen peroxide is employed in a non-in-situ process, feed streams ofoxygen and/or hydrogen may be introduced. In in-situ processes,likewise, a peroxide feed stream may be additionally introduced.

The reactor is maintained at a suitable temperature, as describedpreviously, and a product take-off stream, containing alkylene oxideproduct, alkylene oxide equivalents, solvent, catalyst and catalystfines, etc., is continuously removed from the reactor. From this productstream, large size catalyst particles, i.e. those having a size of >1μm, preferably greater than 2 μm, may be recycled to the reactor, havingbeen separated by conventional separating techniques, while catalystfines, particularly those having a particle size <0.5 μm, morepreferably <0.2 μm, are discarded or used as raw material for additionalcatalyst synthesis. In some processes, the product stream will containsubstantially no catalyst particles, or only catalyst “fines,” the bulkof the catalyst particles remaining in the reactor.

Alkylene oxide product is separated by distillation from the remainingnon-solid components of the product stream, and reactor dispersionmedium/solvent is advantageously recycled, any loss being made up of“make-up” solvent.

In the case of in-situ reactions, it is preferable that the reactiontake place at relatively high pressure, i.e., at 50 to 1500 psig,preferably 100 to 500 psig, and most preferably 100-200 psig and thatsubstantially pure hydrogen and oxygen feeds be introduced into thereactor. While introduction of nitrogen or other inert gas is notprecluded, obtaining effective concentration of hydrogen and oxygen at agiven reactor pressure is rendered more problematic.

The gas oxygen and hydrogen partial pressures are adjusted to preferablyproduct a gas composition below the explosion limit. Oxygen partialpressure is preferably 3 to 50 psig (122 to 446 kPa), more preferably 5to 30 psig (135 to 308 kPa), and most preferably 5 to 20 psig (135 to239 kPa), while the hydrogen partial pressure is preferably 2 to 20 psig(115 to 239 kPa), more preferably 2 to 10 psig (115 to 170 kPa), andmost preferably 3-8 psig (122 to 156 kPa). Hydrogen and oxygen notreacted are preferably burned as fuel, rather than being recompressedand reused. However, it is also possible to recycle these components.

EXAMPLE 1

Titanium Silicalite Large Crystal Synthesis, Method 1

To a 3-neck flask is charged 51.06 g distilled water which is thencooled with agitation to 5° C. by means of an ice/water bath. A nitrogenblanket is established with an N₂ feed rate of 150 cm³/m. To the cooledwater, 4.4955 g titanium (IV) isopropoxide (98%, Strem 93-2216) isadded, with vigorous stirring, following which 9.102 g 30% hydrogenperoxide is added to the flask over 15 min with very vigorous stirring.The flask is stirred for an additional 10 minutes at 5° C. The color ofthe solution turns yellow upon addition of the hydrogen peroxide, thengold and finally orange. To 254.237 μm of aqueous ammonia is added45.763 g deionized water to form a 25 wt. % aqueous ammonia solution.The flask is removed from the ice bath, and 250.88 g of the 25% aqueousammonia is added with continuous stirring. The solution becomes palegreen with some white precipitate. The contents are stirred for 10minutes, then heated to 80° C. and stirred at this temperature for 3hours. The heat source is removed, and stirring continued overnight withnitrogen purge at 125 cm³/m. The flask is weighed, and the remainder ofthe 25% aqueous ammonia added. The contents are stirred at high speedfor 80 minutes.

To the flask, a mixture of 16.432 g tetrapropylammonium bromide solutionin 49.75 g distilled water is added rapidly with sustained agitation. Tothe contents, 23.3 μg Aerosil® 380 silica (Degussa) is then added, andmixed well.

The entire contents of the flask are transferred to a clean,Teflon-lined, unstirred 1000 ml autoclave which is flushed with nitrogenfor 3-5 minutes at 100-150 cm³/min to displace oxygen from the headspace. Any positive pressure is released, and the autoclave sealed. Theautoclave is heated to 185° C. and stirred at autogenous pressure forapproximately 8 days. The autoclave is slowly cooled to roomtemperature, and the solid product isolated as a wet filter cake on anominal 5 μm filter, redispersed in 300 ml of 80° C. distilled water,agitated vigorously, and again filtered. This distilled water wash isrepeated twice more, following which the catalyst is dried at 60° C.under vacuum overnight. The material is calcined for 4 hours at 110° C.in a Ney oven, followed by calcining at 550° C. for 6 hours in air.Prior to use, the subject invention catalysts were slurried in water andoptionally filtered on 0.45 μm, 0.8 μm, or 5.0 μm filters, retaining thefiltercake (and thus the larger particles).

In the general procedure set forth heretofore, the weight percentage ofTi may be adjusted by increasing or decreasing the amount of titanium(IV) isopropoxide initially added to the flask. The practical limit ofTi incorporation into the zeolite framework is circa 2.0 weight percent,according to the literature. Use of higher levels of titanium are saidto result in anatase formation, which is stated to reduce yield inepoxidation with small (0.2 μm) crystals. Large crystals have beenprepared with titanium contents of from about 1.3 to about 4 weightpercent. It should be noted that the Teflon liner of the autoclaveshould be scrupulously cleaned between catalyst preparation, or a newliner installed.

COMPARATIVE EXAMPLE C1

A titanium silicalite catalyst having a mean particle size of 0.2 μm isprepared by methods of the prior art employing tetraethylorthosilicateas the silica source. See, e.g., U.S. Pat. No. 4,410,501, Example 1.

EXAMPLES 2-7 AND COMPARATIVE EXAMPLE C2

Large size titanium silicalites were prepared by the general methoddiscussed previously and compared to a prior art titanium silicalitecatalyst C1 exhibiting typical epoxidation activity and containing 1.1wt. % titanium, all of which is believed to be incorporated as titaniumsilicalite in a zeolitic structure. The various catalysts were tested inthe screening test described previously. The results are presented inTables 1 and 2 together with the analytical and other data believed tobe relevant. Complete elemental analyses were not performed for allcatalysts. Example 7 consisted of large crystals from which fines wereremoved by filtration and tested for activity as Comparative Example C2.

TABLE 1 Large Crystal TS-1 Syntheses and Epoxidation Catalysis CatalystC1 1 2 3 4 Theo. Ti (wt %) NA 1.38 2.76 2.76 1.38 Filter None 0.45 0.8micron 0.8 micron 5 micron micron Elem. an. (wt %) Al <0.01 0.028 NS0.0465 0.042 C 0.39 <0.1 0.39 0.1 Cl <0.01 <0.001 <0.001 <0.001 Cu<0.001 0.0055 <0.001 <0.001 Fe <0.001 0.013 0.015 0.014 <0.001 H 0.11<0.1 <0.1 <0.1 N <0.1 <0.1 <0.1 <0.1 K <0.001 <0.001 0.001 <0.001 Na<0.01 0.018 NA 0.145 0.052 Si 45 46 44 44.3 46 Ti 1.1 1.21 2.68 2.641.24 Mean Length, μm 0.2 12 8.5 6.7 5.8 Mean Width, μm 0.2 5 3.9 2.4 1.7Mean Thickness, 0.2 1.7 0.87 0.78 0.52 μm N₂ sur. area NA 287 NA 316 371(m²/g) Estimated Ti in 100 40 48 41 52 TS-1 framework relative to Ti(%)¹ Estimated Ti in 1.1 0.478 1.29 1.09 0.644 TS-1 framework (wt %)¹H₂O₂ conv (%) 43 17.1 38.3 33.7 24.6 PO (mmole) 18.50 8.647 15.35 14.7910.45 POE (mmole) 19.43 9.116 18.21 16.78 12.03 POE selectivity 75.6285.87 76.78 79.19 79.54 relative to H₂O₂ (%) ¹Infra red spectroscopyyields a peak whose area is a proportional response to the concentrationTi which is tetravalent and in the titanium silicalite zeolite latticeand another peak whose area is proportional to the concentration ofsilicon in the material. The ratio of these two peak areas isproportional to the concentration in wt % of Ti which is in the TS-1framework. These two variables have been correlated using TS-1 samplesof known Ti content which have been # shown by diffuse reflectance ultraviolet spectroscopy and Xray spectroscopy to contain all the Ti in azeolite framework. This method allows the Ti in the TS-1 framework ofother samples to be determined and the proportion of that relative tothe total Ti may be computed from the elemental analysis.

TABLE 2 Large Crystal TS-1 Syntheses and Epoxidation Catalysis CatalystC1 5 6 C2 7 Theo. Ti NA 1.38 1.38 4.04 4.04 (wt %) Filter None 5 micron5 micron 5 micron 5 micron Elem. an. (wt %) Al <0.01 0.053 0.068 NA NA C0.39 Cl <0.01 Cu <0.001 Fe <0.001 0.012 0.014 0.011 NA H 0.11 N <0.1 K<0.001 Na <0.01 0.054 0.065 NA NA Si 45 46 45 44 NA Ti 1.1 1.14 1.25<0.001 NA Mean Length, 0.2 8.5 8.1 10.8 NA μm Mean Width, 0.2 2.6 1.62.5 NA μm Mean Thick- 0.2 0.72 0.62 0.81 NA ness, μm N₂ sur. area NA 351NA 305 NA (m²/g) Estimated Ti 100 64 46 21 NA in TS-1 framework relativeto Ti (%)¹ Estimated Ti 1.1 0.729 NA 0.639 NA in TS-1 framework (wt %)¹H₂O₂ conv (%) 43 21.34 19.98 7.09 32.08 PO (mmole) 18.50 8.00 7.91 10.6614.20 POE (mmole) 19.43 9.76 9.38 11.85 16.69 POE selectivity 75.6274.66 76.6 NA 85.10 relative to H₂O₂ (%)

Tables 1 and 2 indicate that the large size titanium silicalitecatalysts have slightly lower activity than the very small prior artcatalysts. However, the decrease in activity is nowhere near thatexpected in view of the much larger catalyst particle size. Examples 2and 3, for instance, exhibit an average loss in hydrogen peroxideconversion of only about 16%, while selectivity to propylene oxideactually increased somewhat. It is also surprising that the large sizetitanium silicalite catalysts showed greater activity when fines areincreasingly removed. For example, the large titanium silicalitescollected on 0.8 and 5 μm filters showed greater activity than thosecollected on 0.45 μm filters. One would expect the catalysts containingmore small particles to exhibit a higher H₂O₂ conversion rate. However,this is not the case. In Example 7 and Comparative Example C2, theactivity of the retains (large crystals) are compared with the activityof the crystals which pass through a 5 μm filter. The former gave anH₂O₂ conversion of 32.08% as compared to 7.09% for the fines, theopposite of what one would expect. The catalyst of Example 6 wasslurried in 98% sulfuric acid, washed, dried at 110° C., and calcined.Prior to this treatment, the catalyst had shown relatively low activity(7.1% H₂O₂ conversion). Washing with sulfuric acid is one way ofincreasing catalytic activity. The titanium silicalite crystals wereprepared by the general method heretofore described, employing LudoxAS40 colloidal silica (DuPont).

EXAMPLES 8-10

A variety of titanium silicalite catalysts were prepared from a silicasource having a low sodium content. Fumed silica (Aerosil® 380, Degussa)was employed as the silica source. In addition to low sodium content,lower iron and aluminum content is present as compared to the Ludox®AS40 colloidal silica employed in the examples of Tables 1 and 2. Thesodium content of Aerosil® 380 is less than 50 ppm as compared to 1300ppm of the colloidal silica. Trials of a variety of titanium silicalitesprepared using a low sodium silica source are compared with aconventional small size titanium silicalite catalyst of the prior art,and subject invention large size titanium silicalite catalysts preparedfrom a “high” sodium silica source. The relevant physical and chemicalproperties and catalytic activity are presented in Table 3 below.

TABLE 3 Large Crystal TS-1 Synthesis and Epoxidation Catalysts CatalystC1 4 5 7 8 9 10 SiO₂ source Low Low Na Low Na Na Theo. Ti (wt %) NA 1.381.38  4.04 4.04 3.03 2.02 Filter None 5 μm 5 μm 5 μm 5 μm 5 μm 5 μmElem. an. (wt %) Al <0.01 0.042 0.053 NA 0.0051 0.0077 <0.002 C 0.39 Cl<0.01 Cu <0.001 Fe <0.001 <0.001 0.012 NA 0.0035 0.0034 0.005 H 0.11 N<0.1 K <0.001 Na <0.01 0.052 0.054 NA <0.005 <0.005 0.005 Si 45 46 46 NA43 44 45 Ti 1.1 1.24 1.14 NA 3.89 2.65 1.95 Mean Length, 0.2 5.8 8.5 NA9.13 8.06 8.32 μm Mean Width, μm 0.2 1.7 2.6 NA 5.27 3.93 2.65 MeanThickness, 0.2 0.52 0.72 NA 1.53 0.811 0.794 μm N₂ sur. area NA 371 351NA 305 305 NA (m²/g) Estimated Ti in 100 52 64 NA 34 57 72 TS-1framework relative to Ti (%) Estimated Ti in 1.1 0.644 0.729 NA 1.321.514 1.396 TS-1 framework (wt %) H₂O₂ conv (%) 43 24.6 21.34 32.0832.52 39.60 34.10 PO (mmole) 18.50 10.45 8.00 14.20 14.69 21.21 16.95POE (mmole) 19.43 12.03 9.76 16.69 16.56 23.72 18.75 POE selectivity75.62 79.54 74.66 85.10 77.44 97.95 88.88 relative to H₂O₂ (%)

The results in Table 3 indicate that by selecting a low sodium silicasource, both H₂O₂ conversion efficiency and selectivity are high ascompared to otherwise similar catalysts prepared from higher sodiumcontent silica. Results at an intermediate Ti level (Example 9) exhibitnearly the same H₂O₂ conversion efficiency as the small titaniumsilicalite catalysts of the prior art (>90% relative to 0.2 μmcrystals), while the propylene oxide equivalents selectively relative tohydrogen peroxide is truly excellent (ca. 98%). The amount of Tiemployed (ca. 4 wt. %) is higher than can be incorporated into a TS-1structure, contrary to the teachings of the prior art which indicatethat non-framework Ti is detrimental.

Titanium Silicalite Crystalline Intergrowth Syntheses, Method 2

For preparation of intergrowths, tetrapropylammonium hydroxide ormixtures of tetralkylammonium hydroxide and tetraalkylammonium halideare used. Silica and titanium sources may be the same as for singlecrystal growth, but preferably used in Method 2 are siloxane/titanatecopolymers such as alkoxysilane/alkyltitanate copolymers. One suchcopolymer is Gelest PSI TI-019, a diethoxysilane and ethyltitanatecopolymer containing 19.4 wt. % silicon and 2.2 wt. % Ti. In general, atetralkylammonium salt and a base are required. Suitable bases includeorganic amines, ammonia, and tetralkylammonium hydroxide.

EXAMPLE 11

An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 6.8 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-109, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with 10 g of 40 wt % aqueous tetrapropylammonium hydroxide (Alfa)and 25 g water. The mixture was stirred and heated to 80° C. to removeethanol by distillation. The volume was reconstituted with additionalwater and the mixture was introduced into a shaker bomb (autoclave)heated at 150° C. for 7 days. The solid product, 2.2 g of a whitepowder, was analyzed and found to contain 37 wt % Si, 1.1 wt % Ti, 9.2wt % C and 0.99 wt % N. The x-ray diffraction pattern was consistentwith pure titanium silicalite (TS-1). Scanning electron microscopy ofthe product indicated that relatively large (ca. 6-7 micron) crystallineagglomerates were produced, consisting of highly intergrown crystals.

EXAMPLE 12

A crystalline titanium silicate ETS-10 (Englehard) containing 66.1 wt %SiO₂, 10.0 wt % Na₂O, and 4.8 wt % K₂O was ion-exchanged three timeswith 1M NH₄NO₃ at 80° C. To 10 g 40% tetrapropylammonium hydroxide(Alfa) in 25 g water, was added 5.0 g of the ion-exchanged product fromabove. The mixture was introduced into a shaker bomb maintained at 180°C. for 5 days. The recovered product was pure titanium silicalite (TS-1)by x-ray diffraction, and analyzed for 39 wt % Si and 1.7 wt % Ti. SEMshowed crystalline agglomerates, in the size of ca. 3 microns, with ahigh degree of intergrowth.

EXAMPLE 13

A mixture was prepared containing 7.14 g TEOS (tetraethylorthosilicate), 7.07 g titanium-(triethanolaminato) isopropoxide (80% inisopropyl alcohol), 21 g water, 7.39 g 40 wt % tetrapropylammoniumhydroxide (Alfa), and 0.43 g HZSM-5 (CBV-10002 from PQ, with Si/A1=255).The mixture was heated in a shaker bomb at 150° C. for 7 days. 2.38 g ofa white solid was recovered, and shown to be pure titanium silicalite(TS-1) by XRD. After calcination in air at 550° C., the solid analyzedfor 41 wt % Si and 1.2 wt % Ti. SEM indicated the presence ofcrystalline intergrowths, 5-10 microns in size.

EXAMPLE 14

A mixture of 3.97 g of an amorphous titanosilicate (containing 7.0 wt %Ti and 38 wt % Si), 10.0 g 40% tetrapropylammonium hydroxide, 23.9 gwater, and 0.4 g HZSM-5 (CBV-10002 from PG, with Si/A1-255) was heatedin a shaker bomb at 180° C. for 4 days. 3.97 g of a white solid wasrecovered and shown to be pure TS-1 by XRD. After calcination in air at550° C., the product analyzed for 1.6 wt % Ti and 41 wt % Si. SEMindicated the presence of crystalline intergrowths, greater than 5microns in size.

EXAMPLE 15

An intergrowth crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 6.99 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with 1.97 g tetrapropylammonium bromide, 0.31 g calcined TS-1 (1.45wt % Ti), 1.02 g 40 wt % aqueous tetrapropylammonium hydroxide (fromAlfa), and 28 g water. The mixture was heated in a shaker bomb at 150°C. for 7 days, and a solid product, 3.56 g, was recovered. The x-raydiffraction pattern was consistent with pure titanium silicalite.Scanning electron microscopy of the product indicated that relativelylarge (ca. 6-8 micron) crystalline agglomerates were produced,consisting of highly intergrown crystals.

EXAMPLE 16

An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 5.99 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc. containing 19.4 wt % Si and 2.2 wt %Ti), which was preheated at 75° C. for 2 hours with 0.33 g of a calcinedTS-1 containing 1.45 wt % Ti, 10.07 g 40 wt % aqueoustetrapropylammonium hydroxide (from Alfa), and 20 g water. The mixturewas heated in a shaker bomb at 200° C. for 2 days, and a solid product,3.1 g, was recovered. The x-ray diffraction pattern was consistent withpure titanium silicalite (TS-1). After calcination at 550° C., theproduct analyzed for 4.0 wt % Ti and 39 wt % Si. Scanning electronmicroscopy of the product indicated that relatively large crystallineagglomerates were produced, consisting of highly intergrown crystals.

EXAMPLE 17

An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 10.03 g of a diethoxysilane-ethyltitanatecopolymer (PS9150, United Chemical Technology, Inc., containing 44-47 wt% SiO₂ and TiO₂ with Si/Ti—12-13), which was preheated under flowingnitrogen at 80° C. for one hour with 0.33 g of a calcined TS-1containing 1.45 wt % Ti, 10.04 g 40 wt % aqueous tetrapropylammoniumhydroxide (from Alfa), and 20 g water. The mixture was heated at 550°C., the product analyzed for 3.5 wt % Ti and 29 wt % Si. Scanningelectron microscopy of the product indicated that relatively largecrystalline agglomerates were produced, consisting of highly intergrowncrystals.

EXAMPLE 18

An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 7.06 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc. containing 19.4 wt % Si and 2.2 wt %Ti), which was preheated at 75° C. for 2 hours with 0.35 g of a calcinedTS-1 containing 1.45 wt % Ti, 10.52 g 40 wt % aqueoustetrapropylammonium hydroxide (from Alfa), and 20 g water. The mixturewas heated in a shaker bomb at 180° C. for 3 days, and a solid product,3.24 g, was recovered. The x-ray diffraction pattern was consistent withpure titanium silicalite (TS-1). After calcination at 550° C., theproduct analyzed for 1.3 wt % Ti and 41 wt % Si. Scanning electronmicroscopy of the product indicated that relatively large crystallineagglomerates were produced, consisting of highly intergrown crystals.

EXAMPLE 19

An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 13.6 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with 2.7 g tetrapropylammonium bromide, 5 g 40 wt % aqueoustetrapropylammonium hydroxide (from Alfa) and 36 g water. The mixturewas stirred and heated to 80° C. to remove ethanol by distillation. Thevolume was reconstituted with additional water and the mixture wasintroduced into a shaker bomb (autoclave) heated at 175° C. for 5 days.The solid product, 5.07 g of a white powder, was analyzed and found tocontain 38 wt % Si, 2.2 wt % Ti, 9.0 wt % C and 0.92 wt % N. The x-raydiffraction pattern was consistent with pure titanium silicalite (TS-1).Scanning electron microscopy of the product indicated that relativelylarge crystalline agglomerates were produced, consisting of highlyintergrown crystals.

EXAMPLE 20

An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 19.98 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with 1.05 g HZSM-5 (from PQ, CBV-10002, Si/A1=255). The mixture washeated at 70° C. for 2 hours, then kept overnight at room temperature.7.37 g of this mixture was then added to 10.0 g 40% tetrapropylammoniumhydroxide (from Alfa) in 20.1 g water. The mixture was introduced into ashaker bomb (autoclave) and heated at 175° C. for 5 days. The solidproduct, 4.14 g of a white powder, exhibited the x-ray diffractionpattern of pure titanium silicalite (TS-1). After calcination at 550°C., the product analyzed for 1.3 wt % Ti and 44 wt % Si. Scanningelectron microscopy of the product indicated that relatively largecrystalline agglomerates were produced, consisting of highly intergrowncrystals.

EXAMPLE 21

An intergrown crystalline titanium silicalite (TS-1) catalyst wasprepared by mixing together 6.86 g of a diethoxysilane-ethyltitanatecopolymer (PSITI-019, Gelest, Inc.) containing 19.4 wt % Si and 2.2 wt %Ti, with a solution of 2.0 g tetrapropylammonium bromide and 20 gconcentrated ammonium hydroxide in 20 g water. The mixture wasintroduced into a shaker bomb (autoclave) and heated at 175° C. for 7days. The solid product, 2.3 g of a white powder, exhibited the x-raydiffraction pattern of pure titanium silicalite (TS-1). Aftercalcination at 550° C., the product analyzed for 4.1 wt % Ti and 42 wt %Si. Scanning electron microscopy of the product indicated that extremelylarge crystalline agglomerates (greater than 20 microns in size) wereproduced, consisting of highly intergrown crystals.

Catalysis:

Propylene Epoxidation with Pre-Formed Hydrogen Peroxide

Intergrown titanium silicalite catalysts were evaluated for epoxidationactivity by the standard screening test described earlier. The resultsare shown below:

Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Catalyst 13 14 15 16 17 18 19 20 H₂O₂46.8 31.0 49.4 54.3 58.9 60.0 45.9 48.8 Conversion (%) PO (mmol) 25.218.7 26.2 30.4 34.0 34.2 25.3 27.2 POE (mmol) 29.3 20.3 28.9 33.3 37.735.6 26.5 29.0

The results indicate even higher activity than that of many 0.2 μmsingle crystals of the prior art, which is highly surprising in view ofthe limited surface area of the intergrown crystals as compared to 0.2μm single crystals.

General Method, Continuous In Situ Epoxidation

For continuous in situ olefin epoxidation, a Pd-treated catalyst isslurried at 100 g catalyst/liter in 75/25 (w/w) methanol/water. Reactantfeeds consist of liquid propylene and a gas mixture comprising O₂, N₂,and H₂. A cylindrical stainless steel pressure reactor is used, with a 2inch diameter Rushton turbine impeller providing agitation. The reactorhas an essentially flat bottom surface, with about ¼ inch radius concaveperipheral chamfers. The impeller is located above the upper active faceof a filter in the form of a ring of sintered 316 stainless steel. Thefiltered fluid passes into a channel which is machined in the filterbody and which passes around the entire ring.

The hydrogen feed is supplied through a port in the base of the vessel.The liquid propylene feed and previously mixed methanol and watersolvent feed are combined externally to the reactor and fed through adip tube to a point above the base of the vessel. Each gas feed ismonitored via a gas mass flow meter, while liquid feeds are monitoredvia liquid mass flow meters. The exit gas and filtered exit liquid areanalyzed every 2 hours by in-line GC.

The reactor liquid level is controlled by measuring the difference inpressure between the oxygen feed gas dip tube, which terminates close tothe base of the vessel, and the head space of the reactor. Thedifferential pressure cell has a range of 20 inches water gauge.Deviations in the level from the controller set point (normally 4.0 to5.0 inches) result in corrective action via the flow rate control valvein the filtered liquid exit line.

The reactor is usually run at 500 psig and 45° C. or 60° C. There is nodraught tube in the reactor and it is intermediate between lab and pilotplant scales. Several in situ runs employing Pd-treated titaniumsilicalite catalyst were made.

EXAMPLE 22

The results are presented in Table 5. In Tables 5 and 6, abbreviationssuch as SPPO, SOPO, etc., refer to selectivity (S) based on propylenefeed (P), hydrogen feed (H) or oxygen feed (O) with respect to theparticular product, i.e. propylene oxide (PO), propylene oxideequivalents (POE), ring opened products (RO:POE minus PO), propane,water, or carbon dioxide. Thus, SPPO is the selectivity (mol/mol) ofpropylene conversion to propylene oxide, while SOPO is the selectivityof oxygen conversion to propylene oxide.

TABLE 5 Continuous Reaction Using Pd on Large TS-1 Crystals (Example 22)2 3 1 Hydrogen Overall After Break-in Feed Run, Maximum POE Best RateAfter Time Period Designation Overall Performance Reduced Break-in Starttime (hr) 25.98 137.97 25.98 End time (hr) 76.00 165.95 165.95 Duration(hr) 50.02 27.98 139.97 Feed ratios Propylene/hydrogen 1.86 2.14 1.92Oxygen/hydrogen 2.00 2.30 2.07 Exit partial pressure (psi) Propylene7.42 12.00 9.59 Oxygen 18.63 19.45 18.90 Hydrogen 2.25 3.37 3.06Conversion (%) Propylene 20.18 9.71 14.40 Oxygen 15.00 16.33 17.06Hydrogen 76.12 62.81 68.84 Rate PO productivity 0.017 0.020 0.019(gmPO/gcathr) RO productivity 0.031 0.022 0.028 (gmPO/gcathr) POEproductivity 0.047 0.042 0.045 (gmPO/gcathr) POE productivity 4.7 4.24.5 (gmPO/liter slurry hr) PO/POE (%) 35.00 48.02 42.66 PropyleneSelectivity SPPO (%) 30.34 39.78 35.75 SPRO (%) 56.93 43.10 48.68 SPPOE(%) 87.28 82.89 84.43 SPPropane (%) 11.76 16.56 14.83 SPCO₂ (%) 0.970.55 0.73 Oxygen Selectivity SOPO (%) 14.45 22.69 18.52 SORO (%) 28.9924.73 25.05 SOPOE (%) 41.45 47.42 43.57 SOH₂O (%) 56.66 51.17 54.84SOCO₂ (%) 1.89 1.40 1.59 Hydrogen Selectivity SHPOE (%) 31.05 25.9326.69 SHPropane (%) 3.18 6.27 4.91 SHH₂O (%) 65.77 67.80 68.40

EXAMPLES 23-26

Additional continuous runs have been conducted employing furthercatalysts. The results are presented in Table 6 below. Example 26employed a 1:1 mixture of two palladium-treated catalysts, whose basecatalysts, prior to Pd-treating, were prepared in the same manner andwith the same reactants and reactant ratios as the base catalyst ofExample 24, i.e. Example 9 of the subject invention. The respective basecatalyst particles had mean dimensions of 9.69×3.65×1.038 μm and5.91×2.66×0.595 μm, respectively. Analysis revealed 3.08 and 3.18 weightpercent titanium as compared to 2.65 weight percent titanium of the basecatalysts of claim 9. Screening test results showed 35.8 and 40.69 H₂O₂percent conversion, and 19.87 and 22.61 mmol POE. POE selectivity was91.42 and 90.89, respectively. The Pd-treated catalysts of Example 26were treated with Pd(NH₃)₄ (NO₃)₂ and calcined as previously disclosed.Pd weight percent was 0.49.

TABLE 6 Example 23 24 25 26 Large TS-1 Prep Example 8 Example 9 — Seetext Mass cat (gm) 16.14 15.2 40.07 37.22 Vol Slurry (ml) 400 400 400400 Cat conc 4.035 3.8 10.02 9.305 (gm/100 ml) Hours on Stream (hr) 23591.23 166 102 Press (psig) 500 500 500 500 Temp (C.) 60 60 60 60 Agit(RPM) 750 750 750 750 Feed 90 methanol 75 methanol 75 methanol 75methanol Composition (wt %) 10 water 25 water 25 water 25 water AmmoniumBicarbonate Feed Zero 71 150 (0-46.5 hr) 2000 (0-48 hr) (ppm in liquidfeed) 285 (46.5-166 hr) 1000 (48-102 hr) Peak POE (gmPO/gmcat hr) 0.070.15 0.055 0.32 At POE peak: 84 SPPOE (%) 93 93 88 60 SOPOE (%) 10 58 4635 SHPOE (%) 5 39 28 Mean POE 0.03 0.107 0.045 NA (gmPO/gmcat hr) Mean:NA SPPOE (%) 10 91 84 NA SOPOE (%) 5 36 44 NA SHPOE (%) 3 22 27

The results indicate that significant in situ epoxidation has occurred.It should be noted that the results are based on a relatively smallscale reactor, using considerable nitrogen in the oxygen feed. In acommercial reactor, both the reactor pressure as well as the partialpressure of oxygen are expected to be changed to higher values, i.e.,using a pure oxygen feed.

EXAMPLE 27 In-Situ Propylene Epoxidation with Hydrogen and Oxygen

To 1 g of intergrown catalyst of Example 11 dispersed in 87 g methanolwas added 0.0181 g palladium tetraamine dibromide dissolved in 20 gwater. This mixture was stirred at room temperature for 2 hours. Thetemperature was then raised to 45° C. and, at atmospheric pressure,flows of 20% H₂/80% propylene at 25 cm³/min and 5% O₂/0.6% CH₄/94.4% N₂at 88 cm³/min were introduced into the stirred slurry. Exit gas flowswere analyzed by on line gas chromatography. At 30 hours on stream, theexit gas contained greater than 1600 ppm propylene oxide.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. A continuous process for the epoxidation of olefins, said processcomprising: a) providing a reactor containing a titanium silicaliteepoxidation catalyst, said titanium silicalite being in the form ofcrystals or crystal intergrowths, said crystals or crystal intergrowthshaving a mean particle size of greater than 2 μm; b) continuouslysupplying olefin to said reactor; c) supplying hydrogen and oxygen tosaid reactor, optionally together with hydrogen peroxide, whereby atleast a portion of said olefin is epoxidized to an alkylene oxide; andd) continuously removing said olefin oxide, and isolating said olefinoxide, wherein the reactor further contains a noble metal catalyst. 2.The process of claim 1, wherein said olefin is an α-olefin.
 3. Theprocess of claim 1, wherein said olefin is propylene.
 4. The process ofclaim 1, wherein at least a portion of said titanium silicaliteepoxidation catalyst is treated to contain a noble metal which iseffective to catalyze formation of hydrogen peroxide from hydrogen andoxygen.
 5. The process of claim 2, wherein said noble metal is selectedfrom the group consisting of palladium, gold, platinum, and mixturesthereof.
 6. The process of claim 4, wherein a noble metal treatedparticulate other than a titanium silicalite crystal or crystalintergrowth is further provided to said reactor.
 7. The process of claim1, wherein said titanium silicalite catalyst comprises intergrowths oftitanium silicalite crystals.
 8. The process of claim 1, wherein saidtitanium silicalite is prepared from a hydrolyzable silica sourcecontaining less than 500 ppm alkali metal.
 9. A process for thecontinuous production of olefin oxides, said process comprising: a)providing a slurry reactor containing titanium silicalite particleshaving a mean diameter greater than 2 μm as a dispersed phase in aliquid continuous phase; b) introducing into said slurry reactor anepoxidizing oxygen source comprising hydrogen and oxygen; c) introducinginto said reactor at least one olefin; d) withdrawing a product streamcomprising liquid continuous phase, olefin oxide, and olefin oxideequivalents; e) separating any entrained catalyst particles from saidproduct stream prior to, during, or after separation of olefin oxidefrom said product stream; f) separating said olefin oxide from saidproduct stream to provide an olefin oxide product; wherein a noble metalcatalyst is further present.
 10. The process of claim 9, wherein saidnoble metal comprises one or more of Pd, Au, or Pt.
 11. The process ofclaim 9, wherein said titanium silicalite particles are titaniumsilicalite intergrowths having a mean particle size of from 3 μm to 30μm.
 12. The process of claim 9, wherein said noble metal is contained inor on said titanium silicalite catalyst.
 13. The process of claim 9,further comprising separating at least a portion of said liquidcontinuous phase from said product stream and recycling said at least aportion of said liquid continuous phase to the reactor as a make-upsolvent stream.
 14. The process of claim 9, wherein said liquidcontinuous phase comprises water, methanol, or a mixture of water andmethanol.
 15. The process of claim 9, wherein an alkali or metal orammonium carbonate or bicarbonate are additionally introduced into saidreactor.
 16. The process of claim 9, wherein said olefin comprisespropylene.
 17. The process of claim 9, wherein said noble metalcomprises palladium, gold, or platinum, or mixtures thereof.
 18. Theprocess of claim 9, wherein an ammonium phosphate or ammonium hydrogenphosphate or mixture thereof are introduced into said reactor.